This invention relates to the field of container inspection, and more particularly, this invention relates to the field of inspecting substantially cylindrical cans with open tops.
Complicated container and can designs may include a substantially cylindrical top having an opening and inside surface. A flange is often formed at the top opening. An example is a standard beverage can, such as used for carbonated drinks and beer. In many can production lines, statistical process control is used for inspecting the containers and/or cans. Every eight hour shift, a number of different cans are selected and the dimensional height measurements and inside and outside diameter at the top opening, as well as the flange width and flange angle, are measured and compared with a standard. If the cans are off tolerance, then the die operation that produces the can upstream and the inspection equipment itself are analyzed and corrected, if necessary.
Recently, the demands brought about by worldwide competition and lower manufacturing and end-user costs require greater control over the can inspection process. Customers now demand 100% inspection of all cans, instead of the statistical process control inspection where in every shift, only a small number of cans are pulled from the processing line and inspected. This demand for inspecting every can is difficult in most high speed can and container manufacturing operations. Often up to 4.5 million cans are manufactured in a 24-hour shift, corresponding to about 50 cans a second. Thus, the cans are moving extremely fast in the processing station and inspection of each can must occur quickly and efficiently.
There are some prior art inspection systems that have been used for different products, such as cigarettes, as disclosed in U.S. Pat. No. 4,906,099 to Casasent, the disclosure which is hereby incorporated by reference in its entirety. Other inspection systems have been used on cans, but do not provide the desired high speed inspection for the top, interior, flange width and angles and elevation, especially in very high speed conveyor systems. Examples include U.S. Pat. No. 5,699,152 to Fedor et al., U.S. Pat. No. 4,924,107 to Tucker, and U.S. Pat. No. 4,697,245 to Kara et al., the disclosures which are hereby incorporated by reference in their entirety. Some of these systems are not amenable to high speed inspection of both top and sides of cans.
It is therefore an object of the present invention to provide a system and method for inspecting containers and cans, such as the type of beverage can having an inside surface and substantially cylindrical top opening and flange formed at the top opening, which allows inspection of every can at high operating speeds.
It is still another object of the present invention to provide a system and method for inspecting containers and cans that minimizes system complexity while allowing high speed inspection.
In accordance with the present invention, a system allows inspection of containers and cans at high operating speeds such as 50 cans a second. A conveyor advances a plurality of containers along a predetermined path of travel into an inspection area, where an inspection station is positioned. Each container includes an inside surface and a substantially cylindrical top opening and a flange formed at the top opening. In the case of cans, the container is cylindrically configured. A sensor senses when a container has advanced into the inspection area. At least one light source illuminates the exterior of the container and the interior of the container through the top opening after sensing that a container has advanced into the inspection area. A camera is located at the inspection area and has a field of view looking down into the top opening for obtaining a pixel image of the top and interior of the container.
Opposing side cameras are positioned on respective sides of the conveyor at the inspection area and have a field of view in elevation of the container for obtaining pixel images in elevation of the container. Appropriate processing software, such as operating with a digital signal processor that is connected to the sensor and top and side cameras, process the pixel images and calculate the eccentricity, diameter of the opening and flange width measurements based on the pixel image of the top and interior of the container. The processor also calculates height and flange angle measurements based on the pixel images obtained in elevation of the container. The processor includes a circuit for comparing the calculated measurements to a threshold measurement requirement. Cans can be rejected downstream at an ejection station, such as a pneumatic blow off, if the calculated measurements are not within a threshold measurement requirement.
In accordance with another aspect of the present invention, the system includes a circuit for processing the pixel image obtained from the top camera and calculates the inside and outside diameter of the opening. The system can include a backlight positioned adjacent each side camera and the light source can further comprise a strobe light. The cameras in one embodiment can comprise charge-coupled device (CCD) cameras. The sensor can include a beam sensor having a light source positioned on one side of the conveyor and a light receptor positioned on the other side of the conveyor. The conveyor can be formed to have vacuum holes that draw the can down to secure the can in vertical orientation on the conveyor. It is also possible to blow air upward from the conveyor and have containers moved by pressure from one container against the other. If the containers and cans are positioned in close proximity and even adjacent to each other, a can can be sensed by having a light beam from a light source extend to the light receptor, such as when the open crack area formed between two cans allows a light beam to extend from the light source to the light receptor.
In still another aspect of the present invention, the light source generates light on-axis with a vertically oriented can and into the interior of a can through the top opening after sensing that a can has advanced into the inspection area. The light source could include a beam splitter for providing light that is on-axis with the can. Spot lenses, such as coming from a plurality of fiber optic cables, could be used.
In still another aspect of the present invention, a method of inspection is provided to permit the inspecting of containers at high operating speeds. The method comprises the step of feeding a plurality of containers along a predetermined path of travel into an inspection station. The containers each include an inside surface having a substantially cylindrical top opening and a flange formed at the top opening. The method also comprises the step of sensing a container as it advances into the inspection station and illuminating the exterior of the container and its interior through the opening in response to the sensing of the container. Pixel images of the container can be obtained from the top camera having a field of view looking down into the top opening from two opposing side cameras and having a field of view in elevation onto the container.
The method can also comprise the step of processing the pixel images obtained from the top camera for calculating the eccentricity, the diameter of the opening, and the flange width measurements, and processing the pixel images obtained from the side cameras for calculating the height and flange angle measurements. The calculated measurements can be compared with the threshold measurement requirement and a container can be rejected when the container does not meet the threshold requirement.